Gas generator

ABSTRACT

The present invention provides an end-face-burning gas generator having a simple internal structure for easy manufacture, in which the amount of generated gas can be varied during gas discharge. The present invention provides a gas generator including a housing provided with a gas discharge port, an ignition device provided within the housing, a gas generating agent formed in a lump form and provided within the housing such that the gas generating agent is ignited and burnt, by the ignition device, in an end surface thereof, the gas generating agent having a form or a structure such that a combustion surface area thereof changes as the gas generating agent is being burned.

CROSS REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority under 35 U.S.C. § 119(a)on Patent Application No. 2004-358646 filed in Japan on 10 Dec. 2004 and35 U.S.C. § 119(e) on U.S. Provisional Application No. 60/639,322 filedon 28 Dec. 2004, which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas generator, and more particularlyto a gas generator for use in an air bag system installed in anautomobile.

2. Description of Related Art

A gas generator which is capable of generating a desired amount of gasarbitrarily is used conventionally in various applications such as anair bag apparatus which serves as a safety device in a vehicle, or aside thruster for a flying object including a spacecraft.

An example of a gas generator used in a side thruster or the like for aflying object including a spacecraft is disclosed in JP-A No.2002-204947. The gas generator disclosed in JP-A No. 2002-204947 is anend-face-burning type gas generator in which an end face of a gasgenerating agent burns. More specifically, the end surface of the gasgenerating agent is ignited by an igniter such that end-face-burningprogresses in the direction shown by the arrow in FIG. 1 of JP-A No.2002-204947. The generated gas is discharged from a flow hole to a gasflow pipe via a flow control valve, and is ejected to the outsidethrough the gas flow pipe. In this gas generator, the sectional area ofcombustion during the combustion process is set at a substantially fixedvalue so that a fixed amount of combustion gas is discharged.

Meanwhile, in the case of gas generators that are used in variousapplications, it is sometimes desirable to be able to adjust the amountof gas that is generated during the operating period (i.e. during gasdischarge) at will, depending on the application of the gas generator.

For example, in an air bag apparatus for restraining a passenger duringa vehicle collision, it is desirable that the air bag be inflated in atwo-stage or multi-stage process whereby the inflation speed of the airbag during an initial inflation stage is reduced to prevent an excessiveimpact on the passenger when the air bag deploys, and the air bag isdeployed sufficiently in the latter stage. Accordingly, a gas generator(i.e. a gas generator for generating an air bag-inflating gas) whichgenerates gas in two or more stages, such that gas is discharged slowlyduring the initial stage and in a sufficient amount during the latterstage, has been proposed for use in such an air bag apparatus.

JP-A No. 2001-97175 discloses a dual type gas generator in which aplurality of igniters and gas generating agents that are burnedindependently thereby are disposed in separate combustion chambers, andthe amount of generated gas is adjusted by adjusting the ignition timingof each igniter.

SUMMARY OF THE INVENTION

The invention provides a gas generator containing a gas generating agentthat generates a gas when burned and an ignition device for igniting andburning the gas generating agent in the interior of a housing having agas discharge port, the gas generating agent being formed in lump form,and a combustion restricting member for restricting combustion of thegas generating agent, the member being provided on all surfaces of thegas generating agent other than a combustion starting end surface to beignited and burned by the ignition device, the gas generating agenttaking a form or structure according to which a combustion surface areathereof varies as the gas generating agent is burned.

The invention also provides a gas generator containing a gas generatingagent that generates a gas when burned and an ignition device forigniting and burning the gas generating agent in the interior of ahousing having a gas discharge port, the gas generating agent beingformed in lump form, disposed inside a gas generating agent chamberprovided within a housing and being in a condition enablingend-face-burning, the gas generating agent taking a form or structureaccording to which a combustion surface area thereof varies as the gasgenerating agent is burned.

The invention also provides a gas generator containing a gas generatingagent that generates a gas when burned and an ignition device forigniting and burning the gas generating agent in the interior of ahousing having a gas discharge port, the gas generating agent beingformed in lump form such that all or a part thereof is capable ofend-face-burning, the gas generating agent taking an overall form orstructure (i.e. the entirety of the gas generating agent within thespace storing the gas generating agent)according to which a combustionsurface area thereof varies as the gas generating agent is burned.

The invention also provides a manufacturing method for a gas generatorcontaining a gas generating agent that generates a gas when burned andan ignition device for igniting and burning the gas generating agent inthe interior of a housing having a gas discharge port, the manufacturingmethod comprising the steps of: charging a gas generating agent chamberwith a fluid-state gas generating agent; and curing the fluid-state gasgenerating agent to form a lump-form gas generating agent having acombustion starting end surface and a form or structure according towhich a combustion surface area thereof varies as the gas generatingagent is burned.

The invention also provides a manufacturing method for a gas generatorcontaining a gas generating agent that generates a gas when burned andan ignition device for igniting and burning the gas generating agent inthe interior of a housing having a gas discharge port, the manufacturingmethod comprising the steps of: charging a container formed by a memberthat comprises a gas generating agent chamber, or the interior of acontainer stored in the gas generating agent chamber, with a fluid-stategas generating agent; curing the fluid-state gas generating agent toform a lump-form gas generating agent having a combustion starting endsurface and a form or structure according to which a combustion surfacearea thereof varies as the gas generating agent is burned; andincorporating the container charged with the cured gas generating agentin the interior of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention and wherein:

FIG. 1 shows a sectional view of a gas generator for an air bag in apreferred embodiment;

FIG. 2 shows a curve of internal tank pressure when the gas generatorshown in FIG. 1 is burned in a closed tank;

FIG. 3 shows a sectional view during an operation of the gas generatorshown in FIG. 1;

FIG. 4 shows a sectional view of a gas generator in another embodiment;

FIG. 5 shows a curve of internal tank pressure when the gas generatorshown in FIG. 4 is burned in a closed tank; and

FIG. 6 shows a sectional view of a gas generator for an air bag inanother embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a gas generator with which the amountof gas generated in an end-face-burning type gas generator can be variedduring an operation (i.e. during gas discharge).

The present invention also relates to a gas generator in which themanufacture and internal structure of the gas generator are notincreased in complexity, and the weight of the gas generator itself isnot increased.

The present invention also relates to a gas generator comprising anignition device and a lump-form gas generating agent and having asimplified internal structure, with which the amount of generated gascan be varied.

A gas generator according to the present invention realizes the aspectsdescribed above by providing a gas generator which has a simplestructure and is capable of varying an amount of generated gas. In thisgas generator, a gas generating agent is formed or disposed so as toperform the end-face-burning, and the combustion surface area of the gasgenerating agent varies during combustion process of the gas generatingagent.

Furthermore, the present invention provides a gas generator containing,in the interior of a housing having a gas discharge port, a solid,lump-form gas generating agent which generates a gas when burned and anignition device for igniting and burning the gas generating agent,wherein at least one end portion of the gas generating agent serves as acombustion starting end surface that is ignited and burned by theignition device, the surfaces other than the combustion starting endsurface are combustion-restricted such that end-face-burning progressessubstantially from the one end portion toward a final end portion, andthe sectional area of the gas generating agent varies in a combustionprogression direction.

The gas generator according to the present invention uses a lump-formgas generating agent, and therefore has a simple internal structure.Moreover, the lump-form gas generating agent performs end-face-burning,and the combustion surface area thereof is varied over time ascombustion progresses. Hence, the gas generator is capable of varyingthe amount of generated gas. The gas generator of the present inventionwhich exhibits this effect may be used as a general gas generator foruse in various applications, and is particularly suited to use as a gasgenerator for an air bag, which is a device for restraining a passengerin the event of a vehicle collision.

In this gas generator, the entirety of the gas generating agent withinthe space (i.e. the combustion chamber) storing the gas generating agenttakes a form or structure according to which the combustion surface areathereof varies as combustion progresses, and therefore the amount ofgenerated gas can be varied during an operation of the gas generator.

The gas generating agent used in the present invention is formed in a“lump form”. In this specification, the term “lump form” indicates aform in which the end-face-burning to be described below can beperformed, and a form in which end-face-burning is performed in at leastone point at time during combustion of the gas generating agent. Thelump-form gas generating agent is preferably provided such thatapproximately one to three, and a maximum of approximately ten, lumps ofthe gas generating agent are disposed in the gas generator, for example.However, there are no particular limitations on the number of lumps ofgas generating agent used. Moreover, a large number of small-form gasgenerating agents such as pellets, single-perforated forms, and porousforms may be used as a part of the gas generating agent of the presentinvention, similarly to a gas generating agent used in a typical gasgenerator. However, in this case the gas generating agent should containat least a constitutional unit which is formed in lump form so as to becapable of performing end-face-burning, and in containing thisconstitutional unit, the gas generating agent of the present inventiondiffers from a conventional gas generating agent using only a largenumber of small-form agents such as pellets, single-perforated forms,and porous forms. When small-form gas generating agents are used in thepresent invention, the small-form gas generating agents are preferablydisposed such that no gaps occur therebetween.

Conventional, small-form gas generating agents such as pellets,single-perforated forms, and porous forms basically perform alloverburning, whereas the gas generating agent used in the present inventiondiffers greatly from that of a conventional gas generator in that, whenthe gas generating agent is constructed in a plurality units, the endsurface thereof bums from one end portion to the final end portionduring at least one or all of the combustion stages thereof, and whenthe end surface is burning, the other surfaces do not bum (in otherwords, end-face-burning is performed).

Hence, the gas generating agent of the present invention is preferablyformed partially or entirely in a lump form which fills a space forstoring the gas generating agent. The lump-form gas generating agent maybe formed as a single lump from the beginning, or may be formed bybinding a powder or the like, or integrating a plurality of bodies. Thegas generating agent of the present invention may also be formed as aplurality of gas generating agents juxtaposed with no gaps therebetween.Particularly when a plurality of gas generating agents is laminated inthe combustion progression direction of the end-face-burning, aconstitution is possible whereby one of adjacent gas generating agentshas to burn out before the end surface of the other gas generator isexposed. Furthermore, when a plurality of gas generating agents islaminated in a direction which intersects the combustion progressiondirection of the end-face-burning, adjacent gas generating agents arepreferably stacked tightly enough to prevent a flame or the likegenerated by the end-face-burning of adjacent gas generating agents fromentering the gap between the gas generating agents.

For example, the gas generating agent of the present invention may beformed as a substantially cylindrical lump having a through hole or asubstantially columnar lump having no through hole, and having asufficient magnitude to fill a gas generating agent storage chamberwhich serves as the space for storing the gas generating agent.

Further, the gas generating agent of the present invention may employapproximately two to six disk-form gas generating agents stacked withinthe gas generating agent storage chamber. Note, however, that when thegas generating agents are formed in disk-form and stacked, the gasgenerating agents should be formed and disposed such that no grooves,gaps, or the like through which a flame can pass occur between thestacked gas generating agents, and such that end-face-burning can beachieved.

By providing a small number of lump-form gas generating agents, thethickness of each gas generating agent increases, leading to a reductionin variation of the combustion surface area caused by cracks or grindingcaused by the shock of an operation of the ignition device or the like,and hence a stable performance can be maintained.

Moreover, by providing a small number of lump-form gas generatingagents, gaps between adjacent gas generating agents are eliminated, andboth the gas generating agent chamber and the entire gas generatoritself can be reduced in size.

When the gas generating agent is provided in a single lump, the singlelump of gas generating agent is disposed in the gas generating agentchamber in the interior of the housing, and hence handling of the gasgenerating agent during assembly is easy, weighing errors areeliminated, and the performance of the gas generating agent during anoperation can be stabilized.

In the present invention, the gas generating agent formed in lump formas described above should be ignited by the ignition device uponactivation of the gas generator such that end-face-burning, wherebycombustion advances from the ignition point (ignition surface) toward afinal end side, is performed within the space in which the gasgenerating agent exists (i.e. the gas generating agent chamber space orthe combustion chamber). Accordingly, the gas generating agent formed inlump form as described above should be ignited such that combustionbegins from one end portion (the combustion starting end surface)thereof, and such that combustion does not progress from any surfaceother than the one end portion (surfaces other than the combustionstarting end surface). Here, the combustion starting end surface denotesthe surface (or part) of the gas generating agent that is ignited first,and generally corresponds to one of the end surfaces of a gas generatingagent formed in lump form. Which end face corresponds to the combustionstarting end surface is determined on the basis of the manner in whichthe gas generating agent is disposed, its positional relationship withthe ignition device, and so on.

In the present invention, to ensure that combustion begins from the oneend portion (the combustion starting end surface), the ignition devicefor igniting the gas generating agent should be disposed facing the oneend portion (combustion starting end surface) from which combustion ofthe gas generating agent begins, and if not directly facing this one endportion, then the ignition device should be disposed such that thehigh-temperature gas and flame that are combustion products of theignition device reach the one end portion (combustion starting endsurface) of the gas generating agent.

An electric igniter that is activated by an ignition current may be usedalone as the ignition device, or to enhance the explosive power of theelectric igniter, a typically-employed transfer charge (boron niter orthe like) may be used alongside the igniter. There are no particularlimitations on the type and specifications of the transfer charge aslong as it increases the explosive power of the igniter and causescombustion of the gas generating agent.

Further, in the present invention, to ensure that combustion does notprogress from surfaces of the gas generating agent other than the oneend portion (surfaces other than the combustion starting end surface),combustion of the surfaces other than the combustion starting endsurface should be restricted, and these surfaces should not be ignitedby the ignition device.

To restrict combustion of the surfaces other than the combustionstarting end surface, a combustion restricting member(s) which restrictscombustion of the gas generating agent by enveloping the surfaces otherthan the combustion starting end surface may be employed. As thecombustion restricting member, there may be employed a component fordefining the gas generating agent chamber within the housing, acomponent which defines the gas generating agent chamber within thehousing and also constitutes the housing (these components will bereferred to together as “gas generating agent chamber constitutionalcomponents” hereafter), or a separate container which envelops thesurfaces of the gas generating agent other than the combustion startingend surface.

The combustion restricting member is formed from a material and with athickness that prevents direct contact between the combustion productsgenerated by the ignition device and all surfaces of the gas generatingagent other than the one end portion (combustion starting end surface),and preferably a material and thickness that prevent ignition of allsurfaces of the gas generating agent other than the one end portion(combustion starting end surface) by heat transfer and radiation duringcombustion of the gas generating agent from the one end portion(combustion starting end surface) to the final end portion. For example,the combustion restricting member may be formed using a material such asstainless steel, iron, or aluminum, at a thickness (1 mm, for example)which satisfies the above conditions. The combustion restricting memberformed in this manner is disposed to envelop all surfaces of the gasgenerating agent other than the combustion starting end surface, andpreferably in contact with and tightly attached to these surfaces.

For example, when the gas generating agent takes a single-perforatedcylindrical form having a through hole in its center, an inner tubewhich covers the inner peripheral surface of the through hole and anouter tube which covers the outer peripheral surface of the gasgenerating agent are used as the member forming the gas generating agentchamber (the combustion restricting member), and the gas generatingagent is disposed in the interior of the housing in contact with thesetubes. On the other hand, when the gas generating agent takes a columnarform having no through hole in its center, a tube covering the outerperipheral surface of the gas generating agent is used as the memberforming the gas generating agent chamber (the combustion restrictingmember), and both the gas generating agent and the tube are disposed inthe interior of the housing such that the gas generating agent contactsthe tube. In so doing, combustion of the gas generating agent does notprogress from the surfaces which contact the inner tube and outer tube,or the surface which contacts the tube, and hence end-face-burning ismaintained.

The term “inner tube” in this specification denotes a cylindrical memberdefining the inside of the gas generating agent storage chamber, and theterms “outer tube” and “tube” denote a cylindrical portion defining theoutside of the gas generating agent storage chamber. All of these tubescover the surfaces of the gas generating agent other than the combustionstarting end surface, and are therefore capable of functioning as thecombustion restricting member.

Note that in order to simplify the internal structure of the gasgenerator of the present invention, a single ignition device ispreferably provided. However, this does not exclude the use of two ormore ignition devices, and when two or more ignition devices are used,the plural ignition devices are disposed to ignite and burn a common endsurface of the same gas generating agent. Hence, even when pluralignition devices are used, the gas generator of the present inventiondiffers from a conventional dual-type gas generator in which theignition device each ignites individual gas generating agents, in thatthe ignition devices ignites and bums a common end surface of the samegas generating agent.

In the present invention, as described above, the gas generating agentperforms end-face-burning whereby combustion progresses from one endportion (the combustion starting end surface) to the final end portion.The gas generating agent is preferably formed such that the combustionsurface progresses in a substantially identical manner regardless of thelocation on the gas generating agent, and such that combustionprogresses in the same direction.

This end-face-burning gas generating agent takes a form or structureaccording to which the combustion surface area thereof (in other words,the surface area of the burning part of the gas generating agent) variesas the combustion goes on. Therefore, the amount of gas generated perunit time can be varied, and as a result the air bag inflation timingand degree of inflation can be optimized.

In other words, in the gas generator of the present invention, the gasgenerating agent performs end-face-burning, and the combustion surfacearea thereof varies during combustion. Therefore, the amount of gasgenerated per unit time can be adjusted at will. In cases such as whenthe air bag inflation speed is to be suppressed at the initial stage ofthe air bag operation to prevent excessive impact on the passenger, andthe air bag is then to be inflated far enough to obtain sufficientrestraint, for example, the gas generator should generate gas gently atthe initial stage, and then generate a sufficient amount of gas at thelatter stage. When gas is to be generated in this manner, the sectionalarea of the burning part of the gas generating agent may be reduced inthe initial stage to reduce the amount of generated gas, and whencombustion has progressed by a fixed distance, the sectional area may beincreased so that a larger amount of gas is generated.

For example, when the gas generating agent is formed in a lump formhaving no cavities or the like in its interior, the surfaceperpendicular to the combustion progression direction serves as theend-face-burning combustion face, and the sectional area thereof (thecombustion sectional area) corresponds to the combustion sectional areaof the end-face-burning. Hence, the amount of generated gas iscommensurate with the sectional area of the surface perpendicular to thecombustion progression direction. Accordingly, by varying the sectionalarea of the surface perpendicular to the combustion progressiondirection of the gas generating agent, the combustion surface areavaries as combustion progresses, and as a result, the amount ofgenerated gas can be adjusted in accordance with the variation in thesectional area.

On the other hand, when the gas generating agent includes interiorcavities or the like, these cavities are exposed as combustionprogresses, and the combustion surface area varies in accordance withthe exposed cavity. Hence, the amount of generated gas varies inaccordance therewith. Therefore, in this case, the amount of generatedgas can be adjusted at will by adjusting the form, formation extent (theproportion of cavities), and so on of the cavities existing in theinterior of the lump-form gas generating agent.

The gas generating agent of the present invention takes a lump-form, andmay also be formed in a single-perforated form having a through holeopened in the center thereof, or a columnar form having no through hole,for example. When the gas generating agent is formed in thissubstantially cylindrical or substantially columnar form and the endsurface thereof is ignited so as to prevent the inner and outerperipheral side faces from burning (to maintain end-face-burning), thevariation in the sectional area which intersects the axial direction ofthe substantially cylindrical or substantially columnar gas generatingagent matches the mass flow as an inflator. Hence in this case, byadjusting the sectional form of the gas generating agent, the operatingperformance of the gas generator (the manner in which the air bag isinflated) can also be adjusted arbitrarily. When the gas generatingagent takes a single-perforated cylindrical form having a through holein its center, the inner peripheral surface of the through hole iscovered by the inner tube, and the outer peripheral surface of the gasgenerating agent is covered by the outer tube, or when the gasgenerating agent takes a columnar form having no through hole and theouter peripheral surface thereof is covered by the tube, the operatingperformance of the gas generator (the manner in which the air bag isinflated) can be adjusted theoretically in any way by adjusting thesectional form of the gas generating agent formed by the inner tube andouter tube or the tube. Note that the form of the sectional area of thegas generating agent is not limited to the circle described above, andmay take a polygonal form (also, a through hole may be formed regardlessof the sectional form).

In the present invention, the combustion surface area of the gasgenerating agent can be varied in the combustion progression directionby varying at least one of the outer diameter of the inner tube and theinner diameter of the outer tube in the axial direction to adjust thesectional area of the gas generating agent, or by varying the innerdiameter of the tube in the axial direction to adjust the sectional areaof the gas generating agent. Accordingly, the gas generator exhibitssimple combustion control.

Moreover, in the gas generator of the present invention, the housingpreferably includes a ceiling plate, a base plate on which the ignitiondevice is disposed, and a peripheral wall portion connecting the ceilingplate and base plate, the ignition device is preferably disposed in theinterior of a member forming an inner peripheral side wall of a gasgenerating agent chamber, the gas generating agent is preferablydisposed so that the axis thereof overlaps the axis of the housing, andthe combustion starting end surface is preferably formed on the ceilingplate side.

The inner tube serves as the member forming the inner peripheral sidewall of the gas generating agent chamber, and by employing the interiorof the inner tube as the ignition device storage chamber storing theignition device, the ignition device can be prevented from protrudingfrom the inflator, and the overall height of the inflator can besuppressed.

Furthermore, in the gas generator of the present invention, thelump-form gas generating agent having a form or structure according towhich the combustion surface area thereof varies during combustion ispreferably formed by charging the gas generating agent storage chamber(the space between the inner tube and outer tube, or the interior of thetube, for example) with a fluid-state gas generating agent and thencuring the gas generating agent, or by charging a container serving asthe member that forms the gas generating agent chamber, or the interiorof a container accommodated the gas generating agent chamber, with afluid-state gas generating agent and then curing the gas generatingagent. Particularly in a case where a fluid-state gas generating agentis cured in a container serving as the member that forms the gasgenerating agent chamber or the interior of a container accommodated thegas generating agent chamber, the container accommodating the cured gasgenerating agent should be incorporated into the interior of thehousing.

A “fluid state” indicates a liquid, powder, colloid, or the like, forexample, and by charging the interior of the gas generating agentstorage chamber (in other words, the combustion chamber) with a gasgenerating agent in this state, and then subjecting the gas generatingagent to a method such as drying, reactive curing, compression, orgelation, the gas generating agent can be formed into a solid orcolloidal block having a substantially cylindrical shape, asubstantially columnar shape, or an arbitrary polygonal shape or angledcylindrical shape.

Further, the gas generating agent in the gas generator of the presentinvention preferably uses one or a mixture of fuels selected from RDX,HMX, 5-nitrotetrazole, 1H-tetrazole, 5-aminotetrazole,1H-tetrazole-1,5-diamine, guanidine nitrate, mono-amine guanidinenitrate, carbodihydrazide, triamine guanidine nitrate,1,2,4-triazole-3-on, 5,5′-bi-1H-tetrazole, dicyandiamide,azodicarbonamide, glycine, semicarbazone, 1H-1,2,4-triazole-3,5-diamine,4-amino guanazole, and guanylurea nitrate, and preferably uses one or amixture of oxidants selected from potassium perchlorate, ammoniumperchlorate, sodium perchlorate, strontium perchlorate, potassiumnitrate, ammonium nitrate, sodium nitrate, and strontium nitrate.

The gas generating agent used in the present invention differs from aconventional gas generating agent, in which all of the used gasgenerating agents (a plurality of gas generating agents such as pelletsor single-perforated forms) burn in a substantially overall burningstate, in that the gas generating agent is formed in lump form andperforms end-face-burning. Therefore, a gas generating agent that hasthe best possible ignitability and combustion performance is preferablyused. Accordingly, the burning rate of the gas generating agent under 10MPa of pressure is preferably not less than 30 mm/sec.

Furthermore, a combustion accelerator is preferably mixed into anddispersed throughout the gas generating agent. One of the followingcombustion accelerators (i) and (ii) may be used as the combustionaccelerator:

(i) a combustion accelerator which contributes directly to combustion ofthe gas generating agent by burning itself in order to further raise thecombustion temperature; and

(ii) a combustion accelerator which does not contribute directly tocombustion of the gas generating agent, but provides conditions foraccelerating combustion.

An example of the combustion accelerator described in (i) is aconventional boron niter or a gas generating agent using nitroguanidineor the like as a fuel and strontium nitrate or the like as an oxidant,which creates an environment with a higher combustion temperature thanthe gas generating agent (the original gas generating agent) into whichthe combustion accelerator is mixed and dispersed.

An example of the combustion accelerator described in (ii) is amicrocapsule, which is a hollow micro-particle, the combustion surfacearea of which increases at one of the combustion stages of the gasgenerating agent(the original gas generating agent) into which thecombustion accelerator is mixed and dispersed, thereby acceleratingcombustion. The microcapsule is preferably formed to bum out or splitopen as the gas generating agent bums.

The combustion accelerator may also be formed to contain metallicparticles.

A combustion accelerator such as that described above, which is used toaccelerate combustion of the gas generating agent, preferably has anaverage particle diameter between 1 to 1000 μn, and more preferablybetween 3 and 500 μm. More particularly, the particle diameter perparticle of the combustion accelerator is preferably between 1 to 1000μn, and more preferably between 3 and 500 μm.

In accordance with the above, as the gas generating agent of the presentinvention, such a gas generating agent may be used that contains 40% byweight of RDX as a fuel, 58% by weight of potassium perchlorate as anoxidant, 1% by weight of sodium carboxymethyl cellulose as a moldingbinder, and 1% by weight of plastic microcapsule as the combustionaccelerator.

Further, the gas generating agent used as the gas generating agent ofthe present invention is preferably provided with a reinforcing memberfor preventing irregularities such as cracks and chips occurring in thecombustion starting end surface of the gas generating agent due to shockgenerated by the impact of an operation of the inflator (an operation ofthe ignition device) or when the inflator is dropped. The reinforcingmember is formed by adhering a film or a porous thin plate to thecombustion starting end surface, or coating the combustion starting endsurface with a hardening resin or the like. By preventing cracks andchips in the gas generating agent, a stable performance can bemaintained without variation in the surface area of the end surface. Adevice such as a film member provided on the combustion starting endsurface of the gas generating agent, or a resin material applied to thecombustion starting end surface of the gas generating agent throughcoating or impregnation and then cured, may be used as the reinforcingmember.

Further, an ignition aid including a material having greaterignitability than the gas generating agent is preferably provided on thecombustion starting end surface of the gas generating agent. A film-formmember coated on one surface or both surfaces thereof with a transfercharge, a porous thin plate member impregnated with a black powder suchas boron niter, or a slurry-form substance mixed with an explosive andcured on the combustion starting end surface of the gas generating agentmay be used as the ignition aid. The ignition aid may also be formed tofunction as a reinforcing member for preventing the occurrence of cracksor chips on the combustion starting end surface of the gas generatingagent caused by shock when the inflator is dropped and so on. Byproviding this ignition aid, ignition of the gas generating agent by theignition device can be assisted.

In the gas generator according to the present invention, the explosiveused in the ignition device is preferably mixed into and dispersedthrough the lump-form gas generating agent as a combustion acceleratorwhich contributes directly to combustion of the gas generating agent byburning itself in order to further raise the combustion temperature.This transfer charge includes mainly a black powder such as boron niter,for example, and has greater ignitability than the gas generating agentso that the ignitability of the gas generating agent can be improved bymixing and dispersing the transfer charge into the gas generating agent.

Further, a gas generating agent having a high combustion temperature maybe used as the ignition aid, and this ignition aid may be provided onthe combustion starting end surface of the gas generating agent.

According to the gas generator of the present invention, a solid,lump-form gas generating agent is used, and combustion progresses fromone end portion thereof to a final end portion while the combustionsurface area varies during combustion. As a result, the amount of gasgenerated per unit time can be varied easily. Particularly when thesurfaces of the gas generating agent other than the end surface arecovered by a constitutional member of the gas generating agent chamberin order to maintain end-face-burning, the amount of generated gas canbe controlled by adjusting the sectional area formed by thisconstitutional member. Hence, the gas generator has a simple internalstructure, is easy to assemble, and has an operating performance thatcan be controlled easily. Furthermore, in order to achieveend-face-burning, the gas generating agent contains a small number oflumps, and no gaps occurs between the gas generating agents. Therefore,the overall size of the gas generator can be reduced.

As above shown, the present invention relates to a gas generator, andmore particularly to a gas generator which is suitable for use in an airbag system installed in an automobile.

EMBODIMENTS OF THE INVENTION

Embodiments of the present invention will be described below on thebasis of the drawings. FIG. 1 is a sectional view of a gas generator foran air bag in an aspect in which the present invention is applied to agas generator for an air bag for a driver side.

A gas generator 100 of this embodiment contains a housing 3 having adiffuser shell 1 and a closure shell 2, an ignition device, or morespecifically an igniter 4 and a transfer charge 5, disposed in a storagespace inside the housing 3, a gas generating agent 6 which is ignitedand burned by the ignition device to generate combustion gas, and anouter tube 8 and an inner tube 9 which define a combustion chamber 7 inwhich the gas generating agent 6 is stored.

The diffuser shell 1 is formed by pressing a stainless steel plate, andincludes a circular portion 12, a peripheral wall portion 10 formed inthe outer peripheral portion of the circular portion 12, and a flangeportion 19 which extends radially outward from the tip end portion ofthe peripheral wall portion 10. Sixteen gas discharge ports 11 having adiameter of 3 mm in this embodiment are arranged with equal intervalscircumferentially in the peripheral wall portion 10. An ignition devicestorage chamber 31 is formed on the inside of the inner tube 9, and theigniter 4 and transfer charge 5 are disposed inside the ignition devicestorage chamber 31.

The closure shell 2 is formed by pressing a stainless steel plate, andincludes a circular portion 30, a central hole 15 formed in the centerof the circular portion 30, a peripheral wall portion 47 formed in theouter peripheral portion of the. circular portion 30, and a flangeportion 20 which extends radially outward from the tip end portion ofthe peripheral wall portion 47. The inner tube 9 is disposed to befitted into the central hole 15. The inner tube 9 includes a steppedportion 50 which engages with the igniter 4, but is formed as a pipewith a fixed thickness and a fixed diameter in the other portion.

The housing 3 is formed as follows: the respective flange portions 19and 20 of the diffuser shell 1 and closure shell 2 are superimposed oneach other and welding 21 is performed, and further the inner tube 9 iswelded to the central hole 15 of the closure shell. The tip end (on thediffuser side) of the inner tube 9 is disposed away from the diffuser.

The outer tube 8 defining the outer peripheral surface of the combustionchamber 7 is joined, by welding, to the circular portion 30 of theclosure 2 at one end, while the opposite end portion (on the diffuserside) is slightly removed from the circular portion 12 of the diffuser 1and left in a non-welded state. Further, the outer tube 8 takes a pipeform having a constant thickness, but varies in diameter at the partdenoted by “a” in FIG. 1.

A single gas generating agent 6 formed in lump-form is disposed in thecombustion chamber 7. The gas generating agent is a hollow columnar bodydisposed such that the inner peripheral surface and outer peripheralsurface thereof contact the inner tube 9 and outer tube 8, respectively.The gas generating agent is also disposed such that a closure side endportion 32 thereof contacts the circular portion 30 of the closureshell, while a diffuser side end portion 40 thereof is removed from thecircular portion 12 of the diffuser shell. In other words, the space towhich the diffuser side end portion 40 of the gas generating agent 6 isexposed communicates with the ignition device storage chamber 31.

The gas generating agent of this embodiment has favorable ignitability,and is formed from 40% by weight of RDX as a fuel, 58% by weight ofpotassium perchlorate as an oxidant, 1% by weight of sodiumcarboxymethyl cellulose as a molding binder, and 1% by weight of plasticmicrocapsule as a combustion accelerator. The gas generating agent usedin this embodiment has 32 mm/sec of the linear burning rate under thepressure of 10 MPa.

The gas generating agent is formed by stirring and melting 1% by weightof carboxymethyl cellulose (“CMC DAICEL #2260” produced by DaicelChemical Industries Ltd.) into 50% by weight of ion-exchanged water at acontrolled temperature of 40° C. so that the two substances are mixedevenly. Once the two substances are mixed evenly, 40% by weight of RDX(a powder produced by Nippon Koki Co., Ltd.), 58% by weight of potassiumperchlorate (“KPD2” produced by Japan Carlit Co., Ltd.), and a plasticmicrocapsule (“MYS F-80E” produced by Matsumoto Yushi-Seiyaku Co., Ltd.)are introduced, and the mixture is stirred for another hour until mixedevenly. The mixture is then left to cool to ambient temperature, wherebya colloidal, hydrous gas generating composition is obtained. Apredetermined amount of the composition is charged into an inflatorcontainer and dried for twenty-four hours at 110° C. to form a moldedproduct.

A coolant/filter 42 is arranged to surround the outer tube 8, definingan annular chamber 41 on the periphery of the tube. The coolant/filter42 is formed by radially laminating a stainless steel plain stitch wiremesh and compressing the laminated wire meshes in the radial directionand axial direction. With the coolant/filter 42, the combustion gasgenerated by combustion of the gas generating agent 6 is cooled, and thecombustion residue contained therein is trapped.

A gap 43 is formed between the peripheral wall portions 10, 47 of thehousing and the coolant/filter 42. The gap 43 forms a gas passage havingan annular radial cross-section on the periphery of the coolant/filter42. Thus the combustion gas passes through the entire portion of thecoolant/filter, enabling effective use of the coolant/filter andeffective cooling and purification of the combustion gas. The cooled andpurified combustion gas passes through the gas passage to the gasdischarge ports 11 in the diffuser shell.

The gas discharge ports 11 in the diffuser shell are sealed by analuminum tape 44 to prevent the infiltration of external moisture intothe interior of the housing 3.

Next, operation of the gas generator shown in FIG. 1 is described. Whenthe vehicle collides, a sensor (not shown) senses the impact andtransmits a signal to a control unit (not shown). The control unitanalyzes the signal, and having determined that the signal indicates animpact, transmits an activation signal to the igniter 4. Thus theigniter 4 is activated and generates high-temperature gas, a flame, ashock wave, and so on.

Upon reception of the high-temperature gas, flame, shock wave, and soon, the transfer charge 5 ignites and burns, generating a flame,high-temperature gas, high-temperature thermo-particles, and so on(“combustion products” hereafter). In the gas generator shown in thedrawing, the diffuser side end portion 40 of the gas generating agent 6communicates with the ignition device storage chamber 31, and thereforethe combustion products generated inside the ignition device storagechamber 31 ignite the end portion 40 of the gas generating agent 6. Notethat the outer peripheral portion and inner peripheral portion of thegas generating agent 6 contact the outer tube 8 and inner tube 9respectively, and the opposite end portion 32 contacts the circularportion 30 of the closure shell 2, and therefore combustion does notoccur from the surfaces of the gas generating agent 6 that contact thesemembers. Hence the gas generating agent 6 performs end-face-burningwhich progresses from the end portion 40 toward the opposite end portion32.

Furthermore, the inner diameter of the outer tube 8 varies in the axialdirection, and therefore the gas generating agent 6 used in the gasgenerator shown in FIG. 1 has a sectional area (sectional area A) whichcorresponds to the diameter denoted by the reference symbol “A” on thediffuser shell 1 side. Meanwhile, the inner diameter of the outer tube 8increases at the curved portion “a” so that the gas generating agent 6has a sectional area (sectional area B) which corresponds to thediameter denoted by the reference symbol “B” on the closure shell 2 side(sectional area A<sectional area B). Hence, as combustion progressesfrom the end portion 40 to the opposite end portion 32, gas is generatedin accordance with the sectional area, leading to an increase in theamount of gas generated per unit time at the curved portion “a”.

FIG. 2 is a graph of a curve (“tank curve” hereafter) showing variationover time in the internal pressure of a sealed tank having a fixedvolume (60 liters, for example) when the gas generator in FIG. 1 isplaced in the tank and burned. A tank which does not exhibit physicalchange or chemical change upon combustion of the gas generator is used.

When the gas generating agent burns upon activation of the gasgenerator, combustion gas is generated from the gas generating agent 6,and the internal pressure of the combustion chamber 7 rises. However,since the lower end of the outer tube 8 and the circular portion 12 ofthe diffuser 1 are not welded together, the housing receives thispressure and deforms as shown in FIG. 3. As a result of thisdeformation, the gap between the lower end of the outer tube 8 and thediffuser shell 1 expands. Next, the gas advances to the coolant/filter42 where residues in the combustion gas are removed and the temperatureof the gas is reduced. The gas then ruptures the sealing tape 44 and isdischarged through the gas discharge ports 11.

Combustion of the gas generating agent advances from the diffuser sideend surface 40 (in other words, the combustion starting end surface),which is ignited by the combustion products produced by the ignitiondevice, and since the sectional area of the gas generating agent (inother words, the combustion surface area) increases at the curvedportion “a”, the amount of gas generated per unit time increases fromthis location. Accordingly, the gradient of the tank curve increasesfrom the point of the curved portion “a” as the amount of gas generatedper unit time increases. Hence, a gas generator which generates gas in asmall amount at the initial operative stage and generates a sufficientamount of gas at the latter stage is obtained. Note that in the gasgenerator of FIG. 1, the gas generating agent 6 contacts the inner tube9 and outer tube 8, and the form of the gas generating agent isdetermined by the form (inner diameter) of the outer tube 8. Hence, byadjusting the form of the outer tube 8, the output of the gas generatorcan be adjusted.

The same effects can be achieved by modifying the form (outer diameter)of the inner tube 9 instead of the outer tube 8, and also by modifyingboth outer tube 8 and inner tube 9.

Further, in the embodiment shown in FIG. 1, a housing, in which thediffuser side end portion of the outer tube 8 is welded to the circularportion 12 of the diffuser shell 1 and a gas flow hole is formed in theouter tube 8 in the vicinity of the diffuser shell 1, may be used.Moreover, the diffuser side end portion of the inner tube 9 may also bewelded to the circular portion 12 of the diffuser shell 1, and aplurality of nozzles connecting the ignition device storage chamber 31to the combustion chamber 7 may be formed in the peripheral wall portionof the inner tube 9 in the vicinity of the diffuser shell.

FIG. 4 is a sectional view of a gas generator 200 for an air bagaccording to another embodiment of the present invention. Identicalcomponents to those shown in FIG. 1 have been allocated identicalreference numerals, and description thereof is omitted.

The gas generator shown in FIG. 4 differs from the gas generator shownin FIG. 1 particularly in the form of an outer tube 38. Accordingly, theform of a gas generating agent 36 which is disposed in contact with theouter tube 38 is also different. Similarly to the gas generator shown inFIG. 1, the transfer charge 5 stored in the ignition device storagechamber is ignited and burned upon activation of the igniter 4, and as aresult, a diffuser side end portion 46 of the gas generating agent 36 isignited and begins to burn. The inner periphery and outer periphery ofthe gas generating agent 36 contact the inner tube 9 and outer tube 38respectively, and a closure side end portion 60 is disposed in contactwith the circular portion 30 of the closure shell 2. Thus the gasgenerating agent can achieve end-face-burning with no combustion fromthe surfaces contacting these members.

The combustion products (a flame, high-temperature gas,thermo-particles, and so on) produced inside the ignition device storagechamber 31 enter the combustion chamber 7 which communicates with thechamber 31, thereby igniting and burning the diffuser side end portion.As combustion progresses, the gas generating agent generates combustiongas which increases the internal pressure of the combustion chamber anddeforms the housing 3, thereby enlarging the gap between the outer tube38 and the circular portion 12 of the diffuser shell 1. The combustiongas flows through this gap toward the filter 42, and as the gas passesthrough the filter 42, it is purified and cooled. The gas is thendischarged through the gas discharge ports 11.

As the end-face-burning of the gas generating agent progresses such thatthe combustion face reaches a curved portion “b”, the inner diameter ofthe outer tube 38 increases. Accordingly, the sectional area of the gasgenerating agent in contact therewith and the combustion surface areaalso increase, leading to an increase in the amount of gas generated perunit time. When combustion progresses further to reach the point of acurved portion “c”, the diameter of the gas generating agent 36decreases, and hence the combustion surface area and the amount of gasgenerated per unit time decrease. At the point of a subsequent curvedportion “d”, the combustion surface area and the amount of gas generatedper unit time increase again.

Similarly to FIG. 2, FIG. 5 is a graph of a curve (“tank curve”hereafter) showing variation over time in the internal pressure of asealed tank having a fixed volume (60 liters, for example) when the gasgenerator in FIG. 4 is placed in the tank and burned.

When the gas generator is activated, combustion of the gas generatingagent advances from the diffuser side end portion 46, and at thelocation of the curved portion “b”, the sectional area of the gasgenerating agent 36 increases, leading to an increase in the amount ofgas generated per unit time from this point. This is reflected in thegraph in FIG. 5. More specifically, the gradient of the tank curve inFIG. 5 (time-internal tank pressure curve) increases from the point ofthe curved portion “b” as the amount of gas generated per unit timeincreases. On the other hand, at the curved portion “c”, the sectionalarea of the gas generating agent decreases, and hence the gradient ofthe tank curve shown in FIG. 5 becomes more gentle from the curvedportion “c”, indicating a decrease in the amount of gas generated perunit time. At the curved portion “d”, the sectional area increasesagain, causing the gradient of the tank curve to become steeper andthereby indicating an increase in the amount of gas generated per unittime. In other words, with the gas generator 200 in FIG. 4, not only cangas be discharged steadily in the initial operative stage, but the gasdischarge amount can also be adjusted in two stages.

Similarly to the gas generator in FIG. 1, the same effects can beachieved by modifying the form (outer diameter) of the inner tube 9instead of the outer tube 38, and also by modifying both the outer tube38 and inner tube 9.

Likewise in FIG. 4, the diffuser side end portion of the outer tube 38may be welded to the circular portion 12 of the diffuser shell 1 and agas flow hole may be formed in the outer tube 38 in the vicinity of thediffuser shell 1. Moreover, the diffuser side end portion of the innertube 9 may also be fixed by welding to the circular portion 12 of thediffuser shell 1, and a plurality of nozzles communicating the ignitiondevice storage chamber 31 with the combustion chamber 7 may be formed inthe peripheral wall portion of the inner tube 9 in the vicinity of thediffuser shell.

FIG. 6 is an axial sectional view of a gas generator which isparticularly suited to use in an air bag apparatus provided on a frontpassenger side. The overall shape of an inflator 300 shown in thisdrawing is formed substantially cylindrical so as to be suitable for usein an air bag system for a front passenger side. A housing 81 forming anouter shell container takes the form of a closed-end cylinder which isclosed at one end 83 and open at an opposite side end portion. A closure82 is attached to the open end portion. Gas discharge ports 80 areformed at equal intervals in the peripheral wall surface of the housing81.

A cylindrical filter 84 is disposed in the interior space of the housing81 formed as described above with a constant gap from the innerperipheral wall of the housing 81. An outer tube 86 is disposed on theinside of the cylindrical filter 84 with a constant gap from the innerperipheral surface of the filter 84, and an inner tube 88 is disposed onthe inside of the outer tube 86 so as to secure a space into which a gasgenerating agent 89 is charged. In this embodiment, the filter 84, outertube 86, and inner tube 88 are all disposed concentrically with thehousing 81. An igniter storage space 90 is formed in the interior of theinner tube 88, and an igniter 91 is disposed in the storage space 90together with a transfer charge 96 that is ignited by the igniter 91. Acommunication hole 92 is formed in the outer tube 86 on the closed endsurface 83 side of the housing 81, and this communication hole 92 issealed by a sealing member (sealing tape or the like) 93. Acommunication hole 94 is also formed in the inner tube 88 on the side ofthe closed end surface 83 of the housing 81. A combustion starting endsurface 95 of the gas generating agent 89 is provided on the side of theclosed end surface 83, and hence end-face-burning is performed from thissurface toward the final end surface (on the closure 82 side).

In the gas generator 300, the transfer charge 96 is burned uponactivation of the igniter 91, and the high-temperature gas generated asa result passes through the communication hole 94 together with heatresidue and the like to reach the combustion starting end surface 95,where combustion of the gas generating agent 89 begins. The gasgenerated as a result raises the internal pressure, thereby rupturingthe sealing member 93, and passes through the communication hole 92 toreach the filter 84. The gas is filtered and cooled as it passes throughthe filter 84, and then discharged through the gas discharge ports 80.

Note that the communication hole 92 may be formed in a position that isoffset from the communication hole 94 to make the communication hole 92less likely to be directly affected by the combustion products that haspassed through the communication hole 94.

In the gas generator 300, the inner diameter of the inner tube 88 islarger on the side of the closed end surface 83 of the housing 81 thanat the part denoted by the reference symbol “a” in FIG. 6, andaccordingly, the sectional area of the gas generating agent 89 is largerat the final end surface side (closure 82 side) than at the referencesymbol a. Hence, when the end-face-burning of the gas generating agentprogresses such that the combustion face reaches the part denoted by thereference symbol “a”, the combustion surface area increases from thispoint, enabling an increase in the amount of gas generated per unittime. Thus the combustion pattern of the gas generating agent can beillustrated by an output curve such as that shown in FIG. 2.

Note that these embodiments were described on the basis of a case inwhich the present invention is applied in particular to a pyrotechnicgas generator using a solid gas generating agent disposed within ahousing. However, the present invention may be used in a hybrid gasgenerator which also uses a pressurized gas.

The invention thus described, it will be obvious that the same may bevaried in many ways. Such variation s are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A gas generator, comprising: a housing provided with a gas dischargeport; an ignition device provided within the housing; a gas generatingagent formed in a lump form and provided within the housing forgenerating a gas by burning, the gas generating agent including acombustion starting end surface that start a combustion thereof by theignition device and having a form or a structure such that a combustionsurface area varies as the gas generating agent is being burned; andcombustion-restricting means provided on all surfaces of the gasgenerating agent other than the combustion starting end surface, thecombustion -restricting means restricting the combustion of the allsurfaces other than the combustion starting end surface.
 2. The gasgenerator according to claim 1, wherein the combustion-restricting meansdefines a gas generating agent chamber for accommodating therein the gasgenerating agent, and an outer peripheral surface, an inner peripheralsurface, and an opposite side end surface to the combustion starting endsurface of the gas generating agent all contact the combustionrestricting means such that the gas generating agent is formedsubstantially columnar form having a through hole which penetrates in anaxial direction thereof.
 3. The gas generator according to claim 2,wherein the combustion-restricting means includes an inner member and anouter member provided in the inner peripheral surface and the outerperipheral surface of the gas generating agent, respectively, and atleast one of an inner diameter of the outer member and an outer diameterof the inner member varies in an axial direction of the housing.
 4. Thegas generator according to claim 1, wherein the combustion-restrictingmeans defines a gas generating agent chamber for accommodating thereinthe gas generating agent, and an outer peripheral surface and anopposite side end surface to the combustion starting end surface of thegas generating agent all contact the combustion-restricting means suchthat the gas generating agent is formed substantially columnar formwithout having a through hole.
 5. The gas generator according to claim4, wherein the combustion-restricting means includes an outer memberprovided in the outer peripheral surface of the gas generating agent,and an inner diameter of the outer member varies in an axial directionof the housing.
 6. A gas generator, comprising: a housing provided witha gas discharge port; an ignition device provided within the housing; agas generating agent formed in a lump form and provided within thehousing such that the gas generating agent is ignited and burnt, by theignition device, in an end surface thereof, the gas generating agenthaving a form or a structure such that a combustion surface area thereofchanges as the gas generating agent is being burned.
 7. The gasgenerator according to claim 6, wherein the combustion surface area ofthe gas generating agent orthogonal to a combustion progressiondirection thereof varies in the combustion progression direction of thegas generating agent.
 8. The gas generator according to claim 3, furthercomprising: an ignition device chamber provided in an inside of theinner member, wherein the ignition device includes an operation-startingmeans for starting an operation of the gas generator and are disposed inthe ignition device chamber at one axial end side thereof, and thecombustion starting end surface exists on the opposite side of the gasgenerating agent chamber to the operation starting device.
 9. The gasgenerator according to claim 2, wherein the gas generating agent existsin a container formed by a member forming the gas generating agentchamber, or in a container stored in the gas generating agent chamber.10. The gas generator according to claim 1, wherein the gas generatingagent contains a fuel and an oxidant, the fuel includes at least onetype selected from the group consisting of RDX, HMX, 5-nitrotetrazole,1H-tetrazole, 5-aminotetrazole, 1H-tetrazole-1,5-diamine, guanidinenitrate, mono-amine guanidine nitrate, carbodihydrazide, triamineguanidine nitrate, 1,2,4-triazole-3-on, 5,5′-bi-1H-tetrazole,dicyandiamide, azodicarbonamide, glycine, semicarbazone,1H-1,2,4-triazole-3,5-diamine, 4-amino guanazole, and guanylureanitrate, and the oxidant includes at least one selected from the groupconsisting of potassium perchlorate, ammonium perchlorate, sodiumperchlorate, strontium perchlorate, potassium nitrate, ammonium nitrate,sodium nitrate, and strontium nitrate.
 11. The gas generator accordingto claim 1, wherein one of the following combustion accelerators (i) and(ii) is mixed into and dispersed throughout the gas generating agent:(i) a combustion accelerator which contributes directly to combustion ofthe gas generating agent by burning itself in order to further raise thecombustion temperature; and (ii) a combustion accelerator which does notcontribute directly to combustion of the gas generating agent, butprovides conditions for accelerating the combustion.
 12. The gasgenerator according to claim 11, wherein the combustion acceleratorcomprises one of the following bases (a) through (c), and the averageparticle diameter of one particle thereof is between 1 and 1000 μm: (a)a base including a fuel and an oxidant and having a higher combustiontemperature than the gas generating agent in which the base is mixed anddispersed; (b) a base including hollow micro-particles, whichaccelerates combustion of the gas generating agent by increasing thecombustion surface area of the gas generating agent at one of thecombustion stages of the gas generating agent in which the base is mixedand dispersed; and (c) a base comprising metallic particles.
 13. The gasgenerator according to claim 1, further comprising: a reinforcing memberfor preventing breakage at the combustion starting end surface isprovided at the combustion starting end surface.
 14. The gas generatoraccording to claim 1, further comprising: an ignition aid containing amaterial that has a greater ignitability than the gas generating agentis provided at the combustion starting end surface.
 15. The gasgenerator according to claim 14, wherein the ignition aid is a film-formmember coated on one surface or both surfaces thereof with a transfercharge.
 16. The gas generator according to claim 14, wherein theignition aid is a porous thin plate member impregnated with a transfercharge.
 17. The gas generator according to claim 14, wherein theignition aid is a slurry-form substance mixed with a transfer charge,which is cured on the combustion starting end surface of the gasgenerating agent.
 18. A method of manufacturing a gas generatorincluding therein a gas generating agent that generates a gas whenburned and an ignition device for igniting and burning the gasgenerating agent in the interior of a housing having a gas dischargeport, comprising the steps of: charging a gas generating agent chamberprovided within the housing with a fluid-state gas generating agent; andcuring the fluid-state gas generating agent to form a lump-form gasgenerating agent having a combustion starting end surface and a form ora structure such that a combustion surface area thereof varies as thegas generating agent is burned.
 19. The gas generator according to claim6, further comprising: combustion-restricting means provided within thehousing, and attaching to and restricting a combustion of all surfacesof the gas generating agent other than the end surface.
 20. The gasgenerator according to claim 6, wherein the gas generating agentcontains a fuel and an oxidant, the fuel includes at least one typeselected from the group consisting of RDX, HMX, 5-nitrotetrazole,1H-tetrazole, 5-aminotetrazole, 1H-tetrazole-1,5-diamine, guanidinenitrate, mono-amine guanidine nitrate, carbodihydrazide, triamineguanidine nitrate, 1,2,4-triazole-3-on, 5,5′-bi-1H-tetrazole,dicyandiamide, azodicarbonamide, glycine, semicarbazone,1H-1,2,4-triazole-3,5-diamine, 4-amino guanazole, and guanylureanitrate, and the oxidant includes at least one selected from the groupconsisting of potassium perchlorate, ammonium perchlorate, sodiumperchlorate, strontium perchlorate, potassium nitrate, ammonium nitrate,sodium nitrate, and strontium nitrate.
 21. A method of manufacturing thegas generator according to claim 18, further comprising: providing,within the housing, a combustion-restricting means such that thecombustion-restricting means attach to and restrict a burning of allsurfaces of the gas generating agent other than the combustion startingend surface.